feat(reports): DATEV-Monatsblatt-Export (Blanko-Vorlage) für Steuerberater

Neuer PDF-Export GET /reports/datev-monthly/export: ein Blatt pro
Mitarbeiter/Monat im Layout der DATEV-Stundenaufzeichnungs-Vorlage
(Beginn/Pause/Ende/Dauer + K/U/UU/F/SA/SU-Kürzel + Bemerkungen +
Summe + Unterschriftsfelder). Führt time_entries, Absences und
Feiertage pro Kalendertag zusammen.

Außerdem: Mustervorlagen für neue Backend-Module (Model/Schema/Router/
Migration/Test) und eine Frontend-Page-Vorlage, abgeleitet vom
hours_payouts-Modul als aktuellstem sauberen Muster.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CviFgc739S89xS97pvjszj

backend/templates/model_template.py

@@ -0,0 +1,67 @@
+"""TEMPLATE – Mustervorlage für ein neues Model.
+
+Anleitung:
+1. Datei nach app/models/<name>.py kopieren
+2. XxxThing, xxx_things, xxx_thing_id konsequent ersetzen
+3. Enum/Felder an das reale Fachmodell anpassen
+4. In app/models/__init__.py importieren (Alembic autodiscovery)
+5. RLS-Policy in der zugehörigen Migration NICHT vergessen (company_id-Fenced) –
+   siehe conftest.py, dort muss die Policy für Tests manuell repliziert werden.
+"""
+import enum
+import uuid
+from datetime import datetime
+from typing import TYPE_CHECKING
+
+from sqlalchemy import DateTime, ForeignKey, String, Text, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    from app.models.user import User
+    from app.models.company import Company
+
+
+class XxxThingStatus(str, enum.Enum):
+    REQUESTED = "requested"
+    APPROVED = "approved"
+    REJECTED = "rejected"
+    CANCELLED = "cancelled"
+
+
+class XxxThing(Base):
+    """Kurzbeschreibung was dieses Model fachlich abbildet."""
+    __tablename__ = "xxx_things"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+
+    # Mandanten-Fenced – Pflicht für RLS-Isolation (DSGVO)
+    company_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=False, index=True
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False, index=True
+    )
+
+    note: Mapped[str | None] = mapped_column(Text)
+    status: Mapped[str] = mapped_column(String(12), nullable=False, default=XxxThingStatus.REQUESTED.value)
+
+    created_by: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=False
+    )
+    decided_by: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL")
+    )
+    decided_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), index=True
+    )
+
+    user: Mapped["User"] = relationship("User", foreign_keys=[user_id], lazy="noload")
+    creator: Mapped["User"] = relationship("User", foreign_keys=[created_by], lazy="noload")
+    decider: Mapped["User"] = relationship("User", foreign_keys=[decided_by], lazy="noload")
+    company: Mapped["Company"] = relationship("Company", lazy="noload")